1. Field of the Invention
The present invention relates to a semiconductor ceramic composition for NTC thermistors, and in particular, a semiconductor ceramic composition for NTC thermistors that contains at least manganese (Mn) and cobalt (Co) as main ingredients.
2. Description of the Related Art
NTC thermistors are used in applications such as temperature detection, and NTC thermistors for temperature detection are required to detect temperatures with high precision or, more specifically, provide deviations of the temperature-resistance value as small as within about ±1%.
There is a problem with the production of NTC thermistors in that the resistance among finished articles varies because of unavoidable variations in manufacturing conditions and other causes. A possible solution is to add heat treatment (annealing) just before the completion of the production of NTC thermistors, as conventional art mentions in paragraph [0011] of Japanese Unexamined Patent Application Publication No. 8-236308. The temperature of annealing for this purpose is usually on the order of 300 to 500° C.
However, annealing may fail to change the resistance of the thermistors to a sufficient extent, depending on the formula of the semiconductor ceramic composition used to make them. For example, the resistance of thermistors based on a composition rich in Co is refractory to annealing and thus annealing cannot be used to adjust the resistance of such thermistors. Ways to adjust the resistance of such thermistors by annealing are therefore in demand.